Ukraine?s HIV epidemic is volatile and expanding, fueled primarily in opioid-dependent people who inject drugs (PWID). HIV prevalence in PWID ranges from 21.3--41.8%,4 accounting for 70% of cumulative and 56% of new infections. Opioid agonist treatments (OAT) using methadone (MMT) or buprenorphine (BMT) maintenance are internationally recognized as effective HIV prevention and treatment of opioid dependence. We have successfully completed and exceeded our original 3 aims, including increasing OAT coverage from 1.5% to 2.7% for the 310,000 PWID who need it. First, using an implementation science framework we qualitatively and quantitatively assessed the client-, program- and policy-level barriers and facilitators to OAT scale-up and effectively used them to change Order 200, the law that governs OAT, such that OAT can now be prescribed outside of addiction specialty settings, including as fee-for-service and pharmacy distribution where patients may receive 10 days of medication without daily supervision. Second, as in the U.S., we have learned that OAT scale-up has been restricted more by moral biases and prejudices than by scientific evidence, requiring innovative patient-centered strategies like shared decision-making (SDM) and user-friendly decision aids to facilitate OAT entry and retention. Third, we developed a national data repository (SyReX) that monitors all OAT and HIV outcomes, allowing us to effectively monitor our implementation strategies. Fourth, HIV+ PWID on OAT were significantly more likely to achieve each level of the HIV care continuum compared to those not on OAT. Fifth, most PWID prefer BMT over MMT and are willing to pay for it, especially if delivered in pharmacies. Sixth, higher OAT doses were the most important contributor to OAT retention (only 24% received high doses), but retention was also higher in PWID on BMT, received OAT in integrated care settings, and differed regionally. Seventh, we developed HIV transmission models for PWID that incorporated incarceration and OAT coverage ? demonstrating that OAT scale-up in prison with continuation post-release was the most effective HIV prevention strategy for prisoners. Eighth, and central to the implementation coaching process, we successfully trained and deployed the NIATx treatment improvement model throughout the country, including over 100 change projects, and significantly increased OAT scale- up at these sites relative to non-NIATx sites by overcoming organizational barriers. This renewal application builds on these accomplishments by directly addressing client-level barriers to OAT by developing and testing an open access, two-step SDM aid, with a focus on HIV+ PWID, to promote OAT scale-up in PWID who have previously or never been on OAT. To overcome program-level barriers, we propose to expand our NIATx program by creating ?regional collaboratives? (a NIATx innovation) to create improved, sustainable models of OAT delivery that focuses on three specific implementation change projects: A) adequate OAT dosing; B) pharmacy- based OAT prescription; and C) HIV/OAT integrated service delivery. Last, we propose to expand our HIV transmission model in PWID to incorporate HCV transmission dynamics and to more comprehensively model the impact and cost-effectiveness of scaling-up interventions to improve OAT scale-up and on improving the HIV continuum of care for PWID in Ukraine. The proposal brings together research and implementation science experts in HIV prevention, infectious diseases, addiction, decision science, NIATx delivery, mathematical and cost-effectiveness modeling and implementation science to provide real-world solutions for PEPFAR?s goals in Ukraine ? to effectively reduce HIV transmission and improve access to HIV treatment nationally and with a focus on PWID.